Stimulation of Pod and Ovule Growth of Soybean, Glycine max (L.) Merr. by 6-Benzylaminopurine

Flowers at distal nodes on soybean racemes usually fail to set pods and subsequently abscise. Physiological and histological studies were performed to determine the influence of 6-benzylaminopurine (BAP) on distal pod development. The pedicels of fully opened flowers on terminal racemes of field-grown IX93-100 soybean plants were treated three times with 200 mg kg-1 BAP in lanolin over a 6-d period. Racemes were then excised and 32P uptake was recorded for each flower position within a raceme; histological features of pedicels and ovules also were determined. Application of BAP increased pod and ovule length, width and weight at all four distal nodes (D, D-1, D-2, D-3) relative to controls treated with lanolin. Length and width of parietal endosperm cells were smaller in BAP-treated ovules at the most proximal node being studied (D-3), and greater numbers of parietal endosperm cells were observed at D-1 and D-3 nodes when compared to lanolin controls. Smaller amounts of starch were found in suspensor cells, endosperm, and integuments of lanolin-treated ovules, and starch depletion over time was observed within starch sheaths of pedicels from lanolin-treated pods when compared to BAP-treated tissues. BAP-treated racemes had more 32P uptake at the four most distal nodes. A higher rate of uptake (cpm mg-1 f. wt) was evident in ovules than in ovary tissues. These results suggest that for racemes otherwise destined to abscise, application of BAP promotes pod set and growth by stimulating ovule development.